well, 400mg elemental calcium is equal to 1000mg calcium carbonate. Each TUMs, I think has 200 mg of elemental calcium. So if you are taking 2000mg of calcium carbonate, you would need 4 Tums. If it's 2000 mg of elemental Calcium, it would be 10-which sounds like too many. I am not that familiar with Tums, and 2000 mg elemental calcium is a lot- the absolute most you should take, in fact, including dietary sources.
I'm not that familiar with Tums, but they are the least expensive source of chewable calcium.